In general, a construction machine is made up of an undercarriage which takes charge of a movement of a machine body and a superstructure mounted on the undercarriage for holding a working device, a power plant, a control/operating device therefor, an operator cab, and others, and so far, a fuel for an engine acting as a power source has been designed to be supplied from a fuel tank located on the superstructure.
A description will be given of, for example, a hydraulic excavator representative of this type of machine. As shown in a perspective view of FIG. 7, the hydraulic excavator is equipped with an undercarriage 101 and a revolving superstructure (superstructure) 102. The undercarriage 101 is of a crawler type, and is made to move the entire hydraulic excavator forwardly/backwardly or change its moving direction by independently rotating right and left running hydraulic motors 114 and 115 simultaneously/alternately for operating sprocket wheels 120 connected thereto and crawlers 121 wound on the sprocket wheels 120.
The revolving superstructure 102 is mounted on the undercarriage 101 through a revolving bearing, not shown, to be revolvable. This revolving superstructure 102 is equipped with a revolving frame, not shown, and at the front side of this revolving frame, there are placed operating cylinders, link devices and others, and further, there are located a front attachment 118 comprising a bucket, an arm, a boom and others and acting as a working device.
Over the entire top surface of the revolving frame, there are mounted a power plant 111, a hydraulic oil tank 112, a fuel tank 113, an operator cab 124 and accessory equipment for controlling/distributing power such as a pressurized oil in the power plant 111 and for carrying out various types of operations.
In addition, these equipment are operated through the use of an operating device situated in the operator cab 124 to control various types of motors and power of pressurized oil supplied under pressure to working cylinders for controlling the operation of the front attachment 118, the revolving operation of the revolving superstructure 102 with respect to the undercarriage 101 and forward/reverse rotation or stop of the hydraulic motors 114 and 115, thereby accomplishing predetermined operations.
A description will be given hereinbelow of a piping system. As shown in FIGS. 7 to 10, on a central portion of an upper surface of a main frame 104 provided for fixedly securing right and left truck frames 103 and 103 into a predetermined related configuration, a swing circle 105 is fixed to firmly support and set a revolving bearing. Moreover, in a hole made at the central portion of the swing circle 105, a swivel joint 106 comprising an inner cylinder 106a and an outer cylinder 106b (see FIG. 10) is located so that its axis coincides with the axis of rotation of the revolving bearing, and these inner cylinder 106a and outer cylinder 106b are in a rotatably and loosely inserted relation, and oil passages constituting a plurality of systems are independently connected thereto at all times. Still moreover, the other end portion of each of these oil passages is made to be connectable to an external line, and the inner cylinder 106a is provided as one with the revolving superstructure 102 side while the outer cylinder 106b is provided with the undercarriage frame 101 side, with they being made to be rotationally movable with respect to each other.
In addition, as FIG. 10 shows, the power of the power plant 111 on the revolving superstructure 102 is transmitted in a manner that a pressurized oil is supplied/returned through the swivel joint 106 to the running hydraulic motors 114 and 115, and pipes 116 and 117 thereof are built in the undercarriage frame 101. In the inner cylinder 106a, pipes for pressurized oils and returned oils are provided between it and a pressurized oil control device of the power plant 111, and on the outer circumference of the outer cylinder 106b, running pipes 116 and 117 are placed, which extend to the rear side of the undercarriage, that is, toward the locations of the sprocket wheels 120. The pipes are independently connected to entries, drain ports, signal ports and others through pressurized oils of the right and left hydraulic motors 114 and 115. The plurality of running pipes 116 and 117, each positioned close to the ground, are bent into a complicated configuration for avoiding a crash against an obstacle on the ground which has not been put in a good condition, and are protected by hollow portions and inside portions of the main frame 104 and the truck frame 103.
Meanwhile, at predetermined positions on the revolving superstructure 102, in addition to a strongly-built bracket for the setting of the front attachment 118, the power plant 111, the hydraulic oil tank 112, the fuel tank 113 and the operator cab 124, there are tightly placed a bonnet belonging to the aforesaid power plant 111, a control unit and a revolution actuators. Moreover, for example, for the improvement of habitability of the operator cab 124, the operator cab 124 is made to have a construction excellent in fully hermetic sealing, dustproof and soundproof and, therefore, the operator cab 124 tend to increase accordingly in size. Still moreover, in a case in which an air conditioning system and others are put in the interior of the operator cab 124, the operator cab 124 is required to have a larger space.
However, due to the relationship between the size of the machine body and the operating capability, limitation is imposed on the outside dimensions of the revolving superstructure 102. In addition, the upgrading of such a type of machine is in rapid progress, and most of automatic control units or associated equipment newly added for the extension of its operating capability require securing a location space on the revolving superstructure 102. Accordingly, there is a need to transfer a part of the equipment/devices, located on the revolving superstructure 102, to another place.
In this case, on the revolving superstructure 102, other than the operator cab 124, the spaces the power plant 111, the hydraulic oil tank 112 and the fuel tank 113 occupy are large, while, from the point of view of the relationship in connection between equipment or efficiency, for the practical use without impairing the operating capability of the machine, it is preferable that, of these equipment, any one of the hydraulic oil tank 112 and the fuel tank 113 is transferred to another location. In particular, in view of the function and efficiency, it is most preferable to transfer the fuel tank 113.
As an example of transferring the fuel tank 113 to the undercarriage as mentioned above, there has been known a technique disclosed in Japanese Utility Model Registration No. 2549354. According to this technique, a fuel tank 107 is accommodated in an inside space between a swing circle 105 and a main frame 104 independently of the main frame 104 as shown in FIGS. 8 and 9, and is constructed as a box-like hollow tank shaped into a doughnut configuration where a broken portion is made in a part of a ring. Moreover, in order to prevent the fuel tank 107 from interfering with running pipes 116 and 117, the fuel tank 107 is configured to surround only approximately a semicircle of a swivel joint 106, and the swivel joint 106 and the running pipes 116 and 117 connected as oil passages to running hydraulic motors 114 and 115 acting as running actuators are fixedly accommodated in the aforesaid broken portion in a state related to each other.
However, since the fuel tank proposed in the foregoing device is accommodated, independently of the main frame 104, in a small area forming an inside space between the swing circle 105 and the main frame 104 which are the structures of the undercarriage, a problem exists in that it is impossible to sufficiently use the space of the undercarriage 101.
On the other hand, although there is an idea in which a structure itself of the undercarriage 101 is made as a fuel tank, difficulty is encountered in preventing the interior of the tank from getting rusty, and in a case in which a crack occurs in the structure in a severe field, there is a possibility that the fuel flows out. Moreover, in this case, there is a problem that dusts such as weld sputtered particles and chips at the manufacturing of the undercarriage remains in the fuel tank.
The present invention has been developed in consideration of the above-mentioned problems, and it is therefore an object of the invention to provide a construction machine capable of making the most of a space of an undercarriage and of having a high-reliability fuel tank unaffected by rust, dust and crack of its structure.